Method for manufacturing a hollow electron-emissive electrode



1959 P. LEMAlGRE-VOREAUX 2, 7 7

METHOD FOR MANUFACTURING A HOLLOW ELECTRON-EMISSIVE ELECTRODE Filed May 10, 1955 J ENAMEL INVENTOR PIERRE LEMAIGRE-VOREAUX BY JAM, fi e M ATTORNEYS United States PatentO METHOD FOR MANUFACTURING A HOLLOW ELECTRON-EMISSIVE ELECTRODE Pierre Lemaigre-Voreaux, Paris, France, assignor to Societe Anonyme pour les Applications de IElectrieite et des Gaz Rares-Etablissements Claude-Paz & Silva, Paris, France Application May 10, 1955', Serial No. 507,285 Claims priority, application France May 20, 1954 7 (Ilaims. (Cl. 117-201) This invention relates to methods of manufacturing a hollow member for supporting the electron emissive material of a hollow electrode of gaseous electric discharge device, said electron emissive material resulting from a process which comprises melting within said member a substance which produces said electron emissive material and said member being at least in part metallic and including at least one narrow slot whereby the interior of said member is in communication with the space surrounding it.

It is known to line the inside of a hollow member with an electron emissive material by a method wherein a substance such as barium dioxide or barium hydrate is melted inside the cavity of said member. This melting may be accompanied by a chemical transformation of the substance and its purpose is to cause said substance, or the compounds into which the melting has converted it, to adhere to the wall of the cavity. After melting, during the pumping of the discharge apparatus, a for mation treatment is carried out which completes the transformation of said substance into an electron emissive material.

The hollow member may be manufactured by swaging, but this method may be difiicult or even impossible for some shapes involving sharp angles and with certain brittle metals such as molybdenum.

If the hollow member is obtained by crimping or nesting, it includes at least one slot at the location of the crimpingor between the nesting parts of the member. This slot is very narrow. butit constitutes, however, a passage through which a portion of the substance intended to provide the electron emissive material escapes from the cavity of the hollow member when it is melted and spreads over the outer surface of the hollow member. This offers several drawbacks. On the one hand, the amount of electron emissive material carried by the electrode is decreased, this decrease being variable from one electrode to another according to the actual size of the slot or slots and on the other hand, the outer surface of the hollow member is fouled since after the formation of the electrode such surface will be covered with electron emissive material, which will facilitate the forming of a cathode spot on said surface, causing a pulverizing of the metal which will deposit on the glass envelope and even causing a cracking of the envelope if the electrode is very close thereto.

One object of the present invention is to avoid the bleeding of the melted emissive material producing sub stance while allowing the utilization of a hollow member obtained by crimping or by nesting or by crimping and nesting.

Features of the method of the invention are the steps of heating enamel to a temperature at which it is able to flow, letting said enamel enter the slot of the hollow member, and allowing said enamel to solidify before the substance which produces the electron emissive material is melted.

It is possible, for instance, to put some enamel powder on the outer metal surface of the hollow member,

then to melt it with a blow-pipe or by heating the member by means of high frequency induction. If the layer of enamel, once it has solidified, covers the entire outer surface of the member, it constitutes an additional safety against the production of cathode spots on said outer surface.

Figure 2 shows the hollow member of Figure l inplan.

The hollow member is shown coated with enamel but not with any electron-emissive material. Furthermore the insulating ring with which the orifice 6 is covered for preventing discharges from starting from the periphery of said orifice is omitted. 1 and 2 denote current lead-in wires for the electrode, which wires, before the enamel is deposited on the hollow member, are welded thereto and are sealed in a bead or in a stern made of the same glass as that of the envelope of the discharge device which will incorporate the electrode.

The hollow member comprises a sleeve 5 and a bot-. tom 3, nested one into the other. The sleeve 5 is in the form of a cylinder which is obtained by rolling a rectangle of molybdenum sheet 0.1 mm. thick, a crimping 7 being incorporated to prevent the cylinder from un rolling. The bottom 3, also. made of molybdenum 0.1 mm. thick, is swaged.

The nesting of the sleeve 5 in the bottom 3 ensures the interconnection of these parts one to the other but 1 In order to make the figures clearer, the clearances in the crimping 7 and between the sleeve 5 and bottom.3 have been greatly exaggerated.

The following method may be used for making the hollow member comprising the parts 3, 5 tight. Very finely powdered enamel is placed in suspension in water. Then a little amount of this suspension is deposited on the outer surface of the hollow member, along the crimping and at the opening of the slot 8.' The member 3, 5 is then heated by a flame, so as to melt the enamel or at least to soften it sufliciently so that it will enter the slots whereafter everything is allowed to cool.

The enamel may be deposited not only in the vicinity of the slots to be stopped, but also over the whole outer surface of the hollow member and on the ends of the current lead-in wires as shown in Figures 1 and 2 in which the enamel is represented in dotted lines designated- 4. This prevents electric discharges from occurring on the outer surface of 'the hollow member.

If the substance which is to be melted inside the hollow member for producing the electron-emissive material is barium dioxide, calcium borate may be used as enamel: when calcium borate is heated to a temperature at which it is cherry red it is sufficiently fluid effectively to enter the slots and at the temperature close to 500 C., to which the hollow member is subsequently raised for melting the barium dioxide it is solid or at least sufliciently viscous Pai ented Feb. 10, s

to prevent its being driven out of the slots by the melted barium dioxide. The melting temperature of calcium borate is not high enough, however, for the molybdenum to be oxidized excessively when calciumboratc has penetrated into the slots.

The manufacturing, of the electrode is completed, for instance, by placing. barium dioxide in the cavity of the hollow member, heating this member with a blowpipe or by means of high frequency induction, at the melting temperature of barium dioxide for a time necessary to ensure a good distribution of the product over the inner wall of the electrode. After cooling, an insulating ring is introduced on the electrode such ring being made of steatite for instance. Subsequently the bead or the stem on which the electrode is. mounted is sealed either to the envelope of a discharge device or to a short length of tube which will be sealed later to such an envelope.

At the temperature to which the electrode will be brought during the formation treatment the enamel will soften, which results in the ring being stuck to the sleeve 5 thus avoidinga possible displacement of said ring when: the discharge device is subsequently handled.

Electrodes thus manufactured, used in low pressure mercury vapour tubes, have a life of the same order as that of cold electrodes while causing a voltage drop little higher than that of filament type hot electrodes.

Numerous modifications to the operating procedure and to the shape of electrode described above may used, within thev scope of the invention. The hollow member for instance may be conical or frustroconical, it may be made of metal. other than molybdenum, such as iron, nickel or tungsten. The substance intended for. producing the electron emissive material may consist o"; barium oxide or barium hydroxide in a substantially hy drated form. These substances may be mixed with one another or with other substances such tantaltun powder, other alkaline-earth compounds, Enamels other than calcium boratemay be used, particularly when a substance other than barium dioxide is to be u ted in the hollow member. The enamel may be depo, ad by dipping all or part of the electrode in a bath of melted enamel.

What I claim is:

1. Ina method for making a seamed hollow electt odc of a gaseous electric. discharge device, whic'lshollow' elf-cc trode is provided on: the inside wall thereof only with electron-emissive material resulting from a process comprising melting on said wall a substance which produces tlte electron-ernissive material, one end of the hollow: elcc- J trode being open: to permit the discharge to pass, and: the wall being formed of at least two pieces of sheet metal impervious. to liquid and nested one within the. other thereby forming a scam, the steps of heating enamel to a flowable temperaturqpermitting said enamel to enter said seam on the whole length thereof, allowing said enamel to. solidify, and then introducing into said hollow electrode and upon the inside wall thereof only the substance which when melted will. produce the electron-emissive material.

2'. In amethod for making a seamed hollow electrode of a gaseous electric discharge device, whichhollow electrode is. provided on the inside wall thereoi only with elec tron-emissive. material resulting from a process comprising melting on said wall a substance which produces the electron-emissive: material, one. end of the hollow electrode being open to permit the discharge to pass, and

the wall being formed of at least two pieces of sheet metal impervious to liquid and nested one within the other thereby forming a seam, the steps of heating enamel to a flowable temperature, permitting said enamel to enter said scam on the whole length thereof and cover substantially the entire outer surface of the wall of said electrode, allowing said enamel, to solidify, and then introducing into said hollow electrode and upon the inside wall thereof only the substance which when melted will produce the electron-emissive material.

3. In a method for making a seamed hollow electrode of a gaseous electric discharge device, which hollow electrode is provided on the inside wall thereof only with electron-emissive material resulting from a process comprising melting on said wall a substance which produces the electron-emissivematerial,.one end of the hollow electrode being open to permit the discharge to pass, and the wall being formed of at least two pieces of sheet metal impervious to liquid and nested one within the other thereby forming a scam, the steps of placing powdered enamel on the outer surface of the wall of said electrode, heating said wall substantially above the incipient softening temperature of said enamel, permitting said enamel to enter said seam on the whole length thereof and to cover substantially the entire outer surface of the wall of said electrode, allowing said enamel to solidify, and then introducing into said hollow electrode and upon the inside wall. thereoi only the substance which when melted will produce the electron-emissive material.

4, In a method for making a seamed hollow electrode of a gaseous electric discharge device, which hollow electrode is provided-on theinside wall thereof only with electron-emissive material resultingfrom a process comprising melting on said wall a substance. whichproduces the electron-emissive material, one end of the hollow electrode being open to permit the discharge to pass, and the wall being open to permit the discharge to pass, and the wall being formed of at least two pieces of sheet metal impervious to liquid and nested one within the other thereby forming a scam, the steps of. heating enamel to a flowable temperature, permitting said cnaznel to enter said seam on the whole length thereof, allowing said enamel to solidify, and then introducing into said hollow electrode and upon the inside wall thereof only the substance which when melted will, produce the electron-emissive material, the flowable temperature of said enamel beingsufiiciently high so that said enamel will not. how at the temperature reached by the hollow electrode during the melting of the substance which produces said electron-emitting material.

5. An enamel for the method. of claim 1 which enamel consists of calcium horate.

A method as set forth in claim 1 in which the substance which produces the electron-emissive material is barium dioxide.

7'. A method as set forth in claim. 1 in which the substance which produces the electron-ernissive material is barium hydrate.

References Cited in the file of this patent UNlTED STATES PATENTS 689,797 Erwin Dec. 24, 1901 2,333,997 Glans Nov. 9, 1943 2,512,769 Crumrine June. 27, 1950 2,698,913 Espersen Jan. 4, 1955 

1. IN A METHOD FOR MAKING A SEAMED HOLLOW ELECTRODE OF A GASEOUS ELECTRIC DISCHARGE DEVICE, WHICH HOLLOW ELECTRODE IS PROVIDED ON THE INSIDE WALL THEREOF ONLY WITH ELECTRON-EMISSIVE MATERIAL RESULTING FROM A PROCESS COMPRISING MELTING ON SAID WALL A SUBSTANCE WHICH PRODUCES THE ELECTRON-EMMISIVE MATERIAL,ONE END OF THE HOLLOW ELECTRODE BEING OPEN TO PERMIT THE DISCHARGE TO PASS, AND THE WALL BEING FORMED OF AR LEAST TWO PIECES OF SHEET METAL IMPERVIOUS TO LIQUID AND NESTED ONE WITHIN THE OTHER THEREBY FORMING A SEAM, THE STEPS OF HEATING ENAMEL TO A FLOWABLE TEMPERATURE, PERMITTING SAID ENAMEL TO ENTER SAID SEAM ON THE WHOLW LENGTH THEREOF,ALLOWING SAID ENAMEL TO SOLIDIFY, AND THEN INTRODUCING INTO SAID HOLLOW ELECTRODE AND UPON THE INSIDE WALL THEREOF ONLY THE SUBSTANCE WHICH WHEN MELTED WILL PRODUCE THE ELECTRON-EMMISIVE MATERIAL. 